Certain magnetic devices, e.g., magnetic random access memory (MRAM) devices, use magnetic memory cells to store information. Each magnetic memory cell typically comprises a submicron piece of magnetic materials, e.g., having the dimensions of 300 nanometers (nm) by 300 nm in area and ten nm thick.
Information is stored in such magnetic devices as the orientation of the magnetization of a storage layer in the magnetic memory cell as compared to the orientation of the magnetization of a reference layer in the memory cell. The magnetization of the storage layer may be oriented parallel or anti-parallel to the reference layer, representing either a logic “0” or a “1.” The orientation of the magnetization of a given layer (storage or reference) may be represented by an arrow pointing either to the left or to the right. When the magnetic memory cell is sitting in a zero applied magnetic field, the magnetization of the storage layer is stable, pointing either right or left. The application of magnetic fields can change the magnetization of the storage layer from right to left, and vice versa, to write information to the magnetic memory cell.
A single reference layer may be replaced by two tightly anti-parallel coupled layers. While two anti-parallel coupled layers perform the same function as a single layer, the combined effective magnetic thickness of the two layers can be reduced (e.g., as compared to a single reference layer), resulting in a reduction in stray magnetic fields being generated (which can affect the storage layer) and a reduction in the susceptibility of the reference layer to perturbations.
A magnetic memory device having two anti-parallel coupled layers, however, is more difficult to set in a desired reference direction (the layers have magnetization properties that are different from a comparable single storage layer device). Namely, as the magnetic field associated with the device changes, the magnetic moments of each of the two anti-parallel coupled layers may “scissor,” both in relation to each other, as well as in relation to the direction of the magnetic field. See for example, M. Pinarbasi et al., AP-pinned Spin Valve GMR and Magnetization, JOURNAL OF APPLIED PHYSICS, vol. 87, n. 9, pgs. 5723–5725, the disclosure of which is incorporated by reference herein, wherein the magnetic moments of two coupled layers are shown to “scissor” in relation to each other with a change in the magnetic field.
This “scissor” effect, which can occur during the fabrication of the magnetic memory device, can lead to deviations in the desired orientation of the magnetization of one or more of the magnetic layers. Such deviations can result in inaccurate and/or unreliable performance of the device.
Therefore, techniques are needed for fabricating magnetic memory devices wherein deviations in the orientation of the magnetization are reduced or eliminated.